1. Field of the Invention
This patent relates to three-dimensional laminated structural/cushioning products and a method of making same. More particularly, this patent relates to laminated structures that are die-cut and formed into three-dimensional shapes more complex than those of laminated structures made by conventional methods.
2. Description of the Related Art
Numerous methods are known to fabricate paper or paperboard into structural and cushioning products. Two primary methods are (1) die-cutting corrugated paperboard panels and folding and gluing the panels to make corrugated boxes, furniture, pallets, reels, packaging, appliance bases, etc.; and (2) die-cutting paper sheets, then laminating and molding the sheets into flat or curved sections for chair backs, seats, etc.
The method of die-cutting corrugated panels and folding and gluing the panels into structures is well known in the corrugated industry. The corrugated panel typically is made of two or more layers of paperboard in alternating sequence of flat paperboard followed by corrugated paperboard. The corrugated paperboard is used to separate the flat paperboard sheets to increase structural efficiency of the panel by placing more material away from the structure""s core. The flat paperboard sheets and corrugated paperboard sheets are bonded together with an adhesive applied to the top and bottom of the corrugations. When bonded together, the sheets form a stiff flat panel.
To produce structural or cushioning articles from the flat panel, the panel is scored along selected lines. The scored lines facilitate folding at specific locations. Folding is accomplished by crushing the corrugated paperboard along the scored lines. After folding the corrugated panel into the desired configuration, overlapping panels may be glued in place.
The basic corrugated xe2x80x9csandwichxe2x80x9d structure is maintained on either side of the scored line. The strength of the finished structure may be enhanced with various folds to include perpendicular ribs or to increase the number of flat and corrugated paper layers. In some instances the structure is made by folding the material, then, if needed, the structure can be unfolded back into a flat sheet for shipping or storage.
In making corrugated structures according to this cut-and-fold method, often the folded score lines are not permanently folded. That is, the folded score lines may act as a living hinge that can be worked back and forth.
In some instances wood or structural foam may be inserted into the corrugated paperboard structure for added strength. In such instances the process of making the basic corrugated structure is similar to that just described.
Unfortunately there are numerous disadvantages to these corrugated paperboard structures. First, the bonding between the flat sheets and the corrugated sheets lies only along narrow corrugated ridges, which results in a relatively weak bond and consequently a relatively weak structure. As will be seen, the three-dimensional paper laminate structure of the present invention has no such weakness.
Second, folding a panel of corrugated paperboard is accomplished by scoring or crushing the corrugated flutes along a line, which in some situations decreases the strength of the structure. With three-dimensional paper laminates made according to the present invention, no crushing occurs, even along fold lines, because the laminate layers fold as a unit. Consequently, the strength of the paper laminate is preserved along the fold line.
Third, corrugated paperboard living hinge lines tend to weaken and become prone to shifting as the lines are worked back and forth. By contrast, with three-dimensional paper laminates such as that disclosed herein, the fold line is rigid and is not easily bent back after the adhesive sets. Consequently, the fold lines of the present invention are strong.
Fourth, corrugated panels are prone to buckling under load. The strength of corrugated panels can be increased by increasing the number of layers of corrugated and flat sheets. However, during bending, the maximum stress is carried by the top and bottom paperboard layers. For corrugated panels, the top and bottom layers are only one paper sheet thick and this sheet is prone to buckling under load.
By contrast, with three-dimensional paper laminates such as that taught herein, most of the core paper material is at the surface of the structure. Where two paper laminates are joined to make a two-sided structure, only the die-cut sections are formed into the core of the structure to provide shear transfer and maintain the distance between the planar surfaces of the two paper laminates, while most of the paper laminate material remains at the planar surfaces. Each planar surface typically has more than two layers of paper laminates bonded together which significantly increases structural stiffness. Structural stiffness, defined as the material modulus of elasticity (E) times the area moment of inertia (I), increases as a cubic function of thickness. Thus, a doubling in the thickness of each planar surface increases the stiffness of the planar surface by a factor of eight.
Finally, corrugated paperboard is prone to surface damage from localized impact because the strength at the surface is based on only one layer of flat paperboard and the corrugated paperboard beneath. Paper laminates, on the other hand, are inherently stronger with each additional laminate layer. With paper laminates, localized crushing or damage due to impact can be minimized by increasing the number of paper layers.
The second conventional method of fabricating paper or paperboard into structural and cushioning productsxe2x80x94die-cutting paper and then laminating and molding it into flat or curved sectionsxe2x80x94is best known in the packaging and furniture industries for making pallet components, chair backs and seats, etc. To make a flat or curved laminated paper structure, multiple sheets of paper are die-cut to final or near-final dimensions. A layer of adhesive or thermoplastic polymer is then placed between each paper layer. If the structure is bonded with a setting adhesive, then before the adhesive sets the layers of paper are placed in a curved mold and pressed and held with pressure until the adhesive sets sufficiently for the structure to be removed and the shape maintained. If the structure is bonded with a thermoplastic polymer, either the layers of paper are preheated sufficiently to allow the plastic to shear or flow and then the laminates are placed into a mold and pressed into shape, or heat is applied in the mold to allow the plastic to flow and the mold is then cooled to set the thermoplastic polymer and hold the paper layers in place.
In either bonding methodxe2x80x94adhesive or thermoplastic polymerxe2x80x94the laminated structure is generally continuous and has a uniform thickness across the curved shape. The exception to the continuous structure may be the inclusion of holes for screw inserts or access openings for hand-holds or the like.
Like corrugated paperboard structures, there are numerous disadvantages to conventional paper laminates. First, it is often necessary to bond conventional paper laminated shapes to a core material to produce a stress skin that has sufficient stiffness, which increases cost and complexity. By contrast, three-dimensional paper laminates that are die-cut and formed according to the present invention to achieve sufficient stiffness do not require bonding to a core material.
Second, conventional paper laminates can have curvatures, but they cannot have sharp complex curves or shapes. The die-cutting and molding process disclosed herein can produce paper laminates having complex out-of-plane structural and cushioning features.
Finally, it is difficult with conventional paper laminates to make out-of-plane structural features. Conventional paper laminates sometimes have access openings, but these are for functional purposes (eg. hand holds) and not for structural purposes. The present invention provides a noncontinuous planar structure having die-cut areas that are formed (pressed) out-of-plane to make structural features such as struts, flanges, bosses and other reinforcement type features.
Thus it is an object of the present invention to provide a three-dimensional laminated structural/cushioning product and method of making same that eliminates many of the disadvantages of conventional corrugated paperboard and laminated products.
A particular object of the present invention is to provide a laminated product having out-of-plane structural features that are more complex than conventional laminated structures.
Another object of the present invention is to provide a die-cut molded laminated structure with superior strength compared to corrugated structures.
Yet another object of the present invention is to provide a die-cut molded laminated structure that can be designed with specific performance or geometric characteristics that are a function of the laminate material, laminate fiber orientation, strut placement and strut shape.
Further and additional objects will appear from the description, accompanying drawings, and appended claims.
The present invention is a three-dimensional laminated structure and method for making same. Structures that may be made using the present method include reel flanges, appliance bases, pallets, furniture and packaging articles. The method is similar to the method for making conventional die-cut paper laminate structures, but includes two additional novel steps. The first additional step is to make specific die-cuts into the laminates where the laminate will be formed out-of-plane. The second additional step is to form the out-of-plane features using a punch and die like assembly.